The present invention relates to storage subsystems, and more particularly to a method and system for dynamically reassigning unused logical volumes on a storage subsystem to an open systems host.
Mainframe computers typically utilize a storage subsystem for storing and accessing huge amounts of data. The storage subsystem is commonly implemented as a direct access storage system (DASD) where many hard disks are organized as a redundant array of inexpensive disks (RAID). The RAID-5 storage architecture, for example, stores data by spreading it over multiple disks along with parity information. If a single disk fails, the parity information allows the system to regenerate that lost data quickly and transparently without interrupting online processing. To the mainframe, a typical storage subsystem RAID data space is one large data space that is accessed through logical volumes.
As data availability needs increase, users see the advantages in making the storage subsystem available not only to mainframe computers, but also to open systems hosts, such as PC""s or workstations running Unix and Windows NT operating systems, for instance. The open systems hosts are connected to the storage subsystem through SCSI (Small Computer System Interface) host adapters, or SCSI controllers. The operating systems of most open systems hosts, however, cannot handle the large data spaces provided by logical volumes. Therefore, on the open systems hosts side, the storage subsystem""s data space is divided into multiple SCSI logical unit numbers (LUNs).
The benefits of making the storage subsystem available to open systems hosts are that it allows large enterprises to consolidate open systems servers into a single location under similar IT (information technology) management, and allows open systems servers to take advantage of advanced storage functions. However, due to the complexities of server consolidation and new enterprise application development, it is very difficult to plan disk storage capacity requirements for the open systems hosts. Consequently, there may be logical volumes on the mainframe side of the storage subsystem that are not used. In order for the open systems host to access this untapped storage space, these unused logical volumes must be reassigned to open systems host LUNs.
Reassigning unused logical volumes from the storage subsystem to the open systems host LUNs has traditionally required temporarily suspending any software processes in the system that will be affected by the reassignment. This includes any software processes on the storage subsystem and mainframe host that access the logical volumes to be reassigned, as well as any software processes on the open systems host that are to be given access to the reassigned logical volumes. After a check is made that the software processes are not currently modifying any data, the software processes are suspended and an operator manually reconfigures both the mainframe and the open systems host. Suspending the processes of a large enterprise system in this manner and making the system unavailable to clients is not only disruptive and inefficient, but also costly.
Accordingly, what is needed is a method and system for dynamically reassigning unused logical volumes on a storage subsystem to an open systems host. The present invention addresses such a need.
The present invention provides a method and system for reassigning unused logical volumes on a storage subsystem to an open systems host that uses logical unit numbers (LUNs). The storage subsystem and the open systems hosts execute respective software processes, and the open systems host is connected to a storage subsystem via an adapter that is controlled from a support controller. The method and system include sending a communication message from the support controller to the adapter, wherein the communication message reassigns the unused logical volumes to LUNs. The method and system further include updating a logical-to-physical mapping stored within the adapter in response to receiving the communication message, whereby storage capacity of the open systems host is increased without suspending the software processes.
According to the method and system disclosed herein, reconfiguring the system with real-time messaging provides enterprises with a flexible and cost effective method for using excess storage-subsystem capacity in support of open systems hosts.